The high density polyethylene (HDPE)/starch composites were prepared by melt blending. The effects of starch contents on the rheological properties, structure, thermal properties, mechanical properties and dynamic mechanical properties of HDPE/starch composites were studied. The results showed that the introduction of starch improved the rheology and toughness of the composites. When the content of starch was 20 wt%, it was uniformly dispersed at micron -scale thickness in HDPE/ starch composites. When the content of starch increased to 30 wt% and 50 wt%, the starch exhibited spherical dispersed phase in HDPE/starch composites, and the average diameter of starch increased from 0.6 μm to 0.8 μm. The breaking strength and breaking elongation of HDPE/ starch blends decreased significantly with the increase of starch content. All the blends with different starch contents were detected to three transition peaks. The γ transition of HDPE at low temperature corresponds to the glass transition peak of polyethylene, it was related to the movement of the amorphous chain segment, and the content of starch had little effect on the γ transition. The β transition was related to starch phase, there was no β transition for pure HDPE, and the peak became wider with the increase of starch content. The α transition in high temperature zone was related to the movement of the restricted chain near the crystallization zone of polyethylene, and it was a complex multiple relaxation process. Introducing a certain content of starch can effectively enhance the rheology and toughness of the composites, and this result can provide a theoretical and technical basis for the high- performance fishing materials based on degradable starch.